An investigation of a compliant interface for press-fit joint replacement

Earlier in vitro studies showed that a compliant layer between a metal surface and trabecular bone improved the load distribution. In this study, the behavior of a compliant layer of Dacron velour was investigated in vivo using a patella resurfacing in a sheep as a model. Bilateral cases were used to compare the velour interface with a direct metal-to-bone interface. For the metal patellas, a fibrous layer developed adjacent to the metal while the underlying bone formed a new subchondral-like layer. With the velour interface, fibrous tissue invaded the velour, followed later by bone, which sometimes reached the metal surface. For follow-ups of 8 months or more, the load across the interface was transferred over localised patches, for both the press-fit and velour interfaces. There was no significant difference in the areas of contact. There was evidence that this was due to the irregularity of the bony surface beneath the fibrous layer, or to bone nodules actually growing up to the metal. It was concluded that in this in vivo model, the velour layer did not retain a more uniform load distribution compared with the press-fit joint, due to the nature of the bone and fibrous tissue that formed at the interfaces.